API Gravity & Crude Oil Density Calculator

What Is API Gravity?

API gravity is the scale the petroleum industry uses to describe how light or heavy a crude oil is compared to water. It was developed by the American Petroleum Institute, which is where the name comes from, and it is really just a more convenient way of expressing specific gravity — a number that tells you whether oil will float on water (it almost always does) and roughly how much refined fuel a barrel of it can produce.

The scale is built so that water sits at exactly 10° API. Anything above 10° is lighter than water and floats; anything below 10° is heavier than water and sinks. Most crude oils traded around the world fall somewhere between 8° and 45° API, with the more valuable, easier-to-refine grades sitting toward the higher end of that range.

This calculator converts freely between API gravity, specific gravity, and density in four different units, tells you instantly whether a given oil counts as light, medium, heavy, or extra heavy crude, and includes a barrels-to-metric-tons converter for anyone working with cargo volumes and shipment weights.

The API Gravity Formula

API gravity is calculated directly from specific gravity (SG), measured at the industry-standard reference temperature of 60°F (15.56°C):

• API Gravity = (141.5 / SG) − 131.5
• Specific Gravity = 141.5 / (API + 131.5)

How to Convert API Gravity to Specific Gravity and Density

Enter an API gravity value in the API Gravity mode above and the calculator immediately returns the matching specific gravity along with density in four common units: kilograms per cubic metre, grams per cubic centimetre, pounds per cubic foot, and pounds per US gallon. This covers pretty much every unit you'll run into on a lab report, a cargo manifest, a refinery data sheet, or an engineering textbook.

The conversion works the other way too. If you already have a specific gravity reading from a hydrometer or a density figure from a lab test, switch to the Specific Gravity or Density mode, plug in your number, and the calculator works out the API gravity and every other density unit for you, along with the crude oil classification.

All of the density figures here use the standard API reference density of water at 60°F — 999.016 kg/m³ — which is the same reference basis used throughout the oil and gas industry, so the numbers line up with what you'd see on an official assay or a cargo inspection certificate.

Light, Medium, Heavy, and Extra Heavy Crude Oil Classification

API gravity isn't just an abstract number — it's the main way the industry sorts crude oil into quality grades, and it has a direct effect on price. Lighter crude flows more easily, needs less processing, and yields a bigger share of high-value products like gasoline and jet fuel when it's refined, so it typically sells at a premium over heavier grades.

• Light crude oil: API gravity above 31.1° — flows easily, refines efficiently, usually commands the highest price
• Medium crude oil: API gravity between 22.3° and 31.1° — the most commonly produced and traded grade worldwide
• Heavy crude oil: API gravity between 10° and 22.3° — thicker, more viscous, needs extra processing or dilution to transport and refine
• Extra heavy crude oil / bitumen: API gravity below 10° — denser than water, often needs to be heated or blended with lighter oil just to flow through a pipeline

Why API Gravity Matters in the Oil Industry

Every barrel of crude oil bought and sold on the global market gets priced partly on its API gravity, because gravity is a fast, reliable stand-in for how much usable fuel a refinery can extract from it. A trader quoting a cargo of Brent or WTI will almost always mention the API gravity in the same breath as the price, because buyers use it to estimate refining yield and transportation cost before a single barrel changes hands.

Petroleum engineers use API gravity to characterize a reservoir the moment new oil is discovered, since it hints at viscosity, the equipment needed to pump it, and how it will behave in a pipeline. Refinery planners use it to decide which units a crude stream should be routed through, and geologists use gravity trends across a field to understand how a reservoir formed. In every one of these situations, this calculator gives you the same figure instantly instead of digging through a reference table or reworking the formula by hand.

Barrels to Metric Tons: Converting Crude Oil Volume to Weight

Crude oil is produced and measured in barrels, but it's shipped, insured, and often taxed by weight in metric tons — so converting between the two is a daily task for oil traders, shipping companies, and customs brokers. The catch is that a barrel of light crude weighs less than a barrel of heavy crude, because they have different densities, which means there's no single fixed conversion factor. You need to know the API gravity (or specific gravity) of the specific cargo first.

The Barrels ⇄ Metric Tons mode above does exactly this: enter a volume in barrels and the API gravity of the crude, and it returns the equivalent weight in metric tons using the same density basis as the rest of this calculator (1 barrel = 158.987 litres, water at 60°F = 999.016 kg/m³). Switch the direction to go from a known tonnage back to barrels, which is useful when a bill of lading lists a cargo weight and you need to work out the loaded volume.

The calculator also shows the 'barrels per metric ton' conversion factor directly, since that's the exact figure oil traders quote on assays and shipping documents — lighter, less dense crude has a higher barrels-per-tonne factor because a tonne of it takes up more volume.

Common Crude Oil Benchmarks and Their API Gravity

A handful of crude oil grades act as global pricing benchmarks, and their typical API gravity is worth knowing as a quick reference point. The figures below are commonly published typical values — actual gravity varies somewhat by field, blend, and individual cargo, so always use the assay figure for a specific shipment when precision matters.

• West Texas Intermediate (WTI): around 39.6° API — a light, sweet US benchmark crude
• Brent Crude: around 38.3° API — the light, sweet North Sea benchmark used to price roughly two-thirds of the world's traded oil
• Bonny Light (Nigeria): around 35.4° API — a light West African crude prized for its low sulphur content
• Arab Light (Saudi Arabia): around 33° API — the reference grade for Saudi Aramco's official selling prices
• Dubai Crude: around 31° API — the key benchmark for medium sour crude priced into Asian markets
• Arab Heavy (Saudi Arabia): around 27° API — a heavier, higher-sulphur Saudi export grade
• Maya (Mexico): around 22° API — Mexico's main heavy export crude
• Western Canadian Select (WCS): around 20.5° API — Canada's heavy oil-sands blend benchmark
• Athabasca Bitumen: around 8° API — extra-heavy oil-sands bitumen that needs diluent just to flow through a pipeline

API Gravity and Temperature

Oil, like almost every liquid, expands when it warms up and contracts when it cools down, so a density or gravity reading taken at a different temperature won't match one taken at 60°F. That's exactly why the industry standardized on 60°F (15.56°C) as the universal reference point for API gravity — it lets everyone compare figures on an equal footing regardless of where or when a sample was actually measured.

In practice, this means an official API gravity or specific gravity value has already been temperature-corrected to the 60°F basis before it ever appears on an assay, lab report, or cargo document. If you're working from a raw hydrometer reading taken at a different temperature, correct it to 60°F first (using an ASTM D1250 volume correction table or equivalent lab procedure) before using it here, so the API gravity and density figures this calculator returns stay accurate and comparable to industry-standard values.

Who Uses an API Gravity Calculator

Petroleum engineers and reservoir geologists use API gravity constantly to characterize newly discovered oil and predict how it will behave in the field. Oil traders and shipping brokers use the barrels-to-metric-tons conversion every time a cargo is bought, sold, or loaded onto a tanker, since freight and insurance are both priced by weight while production and storage are measured by volume.

Refinery engineers use API gravity to route incoming crude to the right processing units and forecast product yield, while students and instructors in petroleum engineering, chemistry, and earth-science courses use it to build intuition for how crude oil grades relate to real-world pricing and refining outcomes. Energy analysts and journalists reference the benchmark values here to put a headline price — 'Brent crude' or 'WTI' — into context against other grades being traded around the world.

A Quick Note on Accuracy

The API gravity, specific gravity, and density formulas used in this calculator are the same industry-standard equations found in API and ASTM petroleum measurement references, and the barrels-to-metric-tons conversion uses the exact 158.987294928-litre US barrel and the standard 999.016 kg/m³ reference density for water at 60°F. That makes this calculator reliable for planning, coursework, quick trading estimates, and general reference use.

For a legally or commercially binding cargo measurement — the kind used to settle a shipment, a customs declaration, or a contract — always use the certified assay figures and correction tables (such as ASTM D1250) provided by an accredited inspection company, since real-world figures can be affected by temperature at the time of loading, sediment and water content, and instrument calibration in ways a simple calculator like this one cannot capture.